Westin gets 1/2 cup three times a day (now that he's 7.5 months, we are about to switch it to 3/4 cup twice a day) depending on the brand of food you use they usually print a guideline of how much to feed on the back according to weight. I'm not saying this is absolute (because honestly, why wouldn't they want you to feed more so you have to buy more) but it is generally a good outline as to how much protein and fat your puppy is getting/needs. I know there is a link somewhere around here on the forums that does a formula/guide for how much to feed... probably try to look around the old posts and see if you can find it!
good luck, and remember that no one knows whats better for your puppy than you and your instinct.